Sintered coaxial plasma gun

ABSTRACT

A plasma gun comprising a rod-shaped inner electrode and a tubular insulator coaxially surrounding it. A second electrode block encloses a portion of the insulator tube. The second electrode comprises a sintered metal having a gas absorbed therein which is releasable to form a plasma. The two electrodes and the tube are arranged to form a flat surface across which an arc can be established between the electrodes in the plasma.

United States Patent Inventor Gerard Verschoore Creteil, France Appl. No. 753,990

Filed Aug. 20, 1968 Patented Aug. 31, 1971 Assignee U.S. Philips Corporation New York, N.Y.

Priority Aug. 22, 1967 France 118566 SINTERED COAXIAL PLASMA GUN 8 Claims, 2 Drawing Figs.

Int. CL. H0lj 17/26 Field olSearch 313/179,

References Cited v UNITED STATES PATENTS 2,640,950 6/1953 Cook 313/179 X 3,030,547 4/1962 Dike et a1. 313/197 X 3,087,092 4/1963 Lafi'erty 313/197 X 3,263,112 7/1966 Kolb et al. 313/198 3,356,897 12/1967 Barr, Jr. et a1. 313/180 X 13,471,736 10/1969 Rich 315/111X Primary Exaniiner- Roy Lake Assistant Examiner- Palmer C. Demeo Anorney Frank R. Trifari ABSTRACT: A plasma gun comprising a rod-shaped inner electrode and a tubular insulator doaxially surrounding it. A second electrode block encloses a portion of the insulator tube. The second electrode comprises a sintered metal having a gas absorbed therein which is releasable to form a plasma. The two electrodes and the tube are arranged to form a flat surface across which an arc can be established between the electrodes in the plasma.

PATENTED'AUGSI i971 3502760 mvsw'ron. GERARD VERSCHOORE SINTERED COAXIAL PLASMA GUN The present invention relates to the production and the ejection of a plasma, i.e. a highly ionized gas, which is preserved by impregnation in a solid substance. The relevant devices are termed plasma guns. At present they are particularly employed in vacuum tubes for physical investigations and have to provide only a very low mean plasma flow. The impregnated medium may be formed by wires enveloped in an insulator which separates them and in which only their ends remain free, as described in British .Patent Specification 821,744 under the title of "Plasma Generator.

The gun is put into operation by the application of an adequate electrical potential difference between the electrodes. An arc is struck which heats the electrodes so that the gas is released (deuterium or hydrogen, for example), which is ionized by the arc. This are generates a magnetic field and it will be obvious that the interaction between this field and the current passing through the arc tends to elongate the electrical circuit completed by said arc, that is to say, to. repel] the are along the straight line of intersection of the plane of symmetry and of the plane of the two wires towards the exterior of the intersection of the wires. This known gun has the following disadvantages:

The impregnation can be carried out only with difficulty due to the solidity of the wires of titanium, which forms the impregnant. It is performed in a furnace at 900 C. prior to the accommodation of the gun in the space of the vacuum tube. Mounting of the gun requires that the wires must come into contact with the atmosphere so that they are polluted by the air, which pollution can afterwards no longer be reduced be degassing.

During the use of the gun the opposite tips of the electrodes are worn off and the gas is soon depleted. Moreover, the technology of assembling the prepared components does not guarantee anything with respect to behavior in vibrations. Furthermore, the adjustment remains critical and is poorly reproducible.

The present invention has for its object to provide a plasma gun which obviates the aforesaid disadvantages.

This plasma gun comprises two electrodes at least one of which is impregnated with the gas which is to be released to form the plasma. An electric insulator separates said electrodes. One of the electrodes has an elongated shape and is enveloped in said insulator, with the exception of its active outer face. The plasma gun is mainly characterized in that the thicknessof said insulator around the elongated electrode is fairly constant and in that said insulator is surrounded by the other electrode, which is formed by a sintered metal impregnated with said gas.

This plasma gun may be furthermore characterized in that a heating filament is incorporated in said sintered electrode.

One embodiment of this plasma gun will now be described with reference to FIGS. 1 and 2 of the drawing, it being understood'that the particular features of this embodiment lie within the scope of the invention.

FIG. 1 is an axial sectional view of the gun which is, in general,-forrned by a body of revolution and FIG. 2 is a plan view thereof.

The elongated electrode 1 is formed by a wire composed of titanium (or molybdenum or thoriated tungsten) having a diameter of 0.5 mm., arranged along the axis of revolution of the gun. This wire is welded at one end to a circular plate 2, which forms the end of a pin 3 of stainless steel or of an Fe-Ni- Co alloy. The wire 1 is surrounded by a tubular sheath 4 of alumina (other ceramic material may also be used) which is metallized at its lower end and welded to the plate 2. The alumina sheath may also be obtained by direct sinteringon the central electrode. At its upper end this sheath is ground to form a convex cone. The sheath itself is surrounded by a block 5 of sintered titanium of a diameter of 0.5 cm, in which a resistance'wire 6 is housed, which serves for electric heating.

The block 5, which forms a deuterium reservoir, is made from titanium particles having dimensions lying between.,40' microns and microns formed by sintering same in vacuo. The power is put into a suitable crucible in which the filament 6, coated with an insulating layer, is disposed previously. The crucible is introduced into a furnace in vacuo, the temperature of which is rapidly raised to 900 C., at which value it is maintained for half an hour. The assembly is then allowed to cool and the atmospheric pressure is reestablished by admitting argon into the furnace. The deuterium impregnation is performed after the final disposition and the electrical connection of the assembly of the components described above in the envelope of the vacuum tube which has to accommodate the gun; a heating current is passed through the filament 6 and the envelope of the tube is exhausted. The gas (argon) adsorbed in the block 5 is thus released; The block is then allowed to cool after the deuterium is introduced into the tube envelope at the appropriate pressure, which depends upon the percentage of impregnation desired. After the termination of cooling and impregnation, the envelope of the vacuum tube is again exhausted and the tube is sealed, after which the gun is ready for use. This impregnation in the space itself in which the gun has to be accommodated removes any risk of pollution by air. Moreover, when the gun hasbeen used to a point of deletion of the deuterium reserve and when the gas pressure in the vacuum tube has risen, it is easy to recharge the gun by. repeating the operations of degassing and impregnation of deuterium.

The heating current is. supplied to the filament 6 by a generator 11. A switch 12 serves for switching on either the heating current or the gun. in the lattercase. the electric power required for the production and the expulsion of the arc (towards the upper end in FIG. 1) is supplied by the discharge of a capacitor 13 via a thyratron 14. The thyratron is switched on by a pulse generator 15. The discharge is performed between the central electrode 1 and the coaxial electrodes, the switch 12 being connected to the electrode 5 via the filament 6, part of the insulation of which is removed during the sintering process in order to establish the electric contact. The capacitor 13 is recharged in a conventional manner by a direct-current generator l6 via a resistor 17. The distance between the electrodes fomied by the wire 1 and the block 5, that is to say, the thickness of the alumina sheath 4 at the surface can be easily adjusted by abrasion of the. upper fiat face of the gun owing to the conical shape of the upper end of said sheath. If, for example, the half-angle at the apex of the cone is 45, an abrasion of 1/50 mms. of the upper face involves an equal increase in apparent thickness of the sheath 4. In practice this thickness is about 0.1 mm. Apart from the easily per,

formed adjustment of the distance between the electrodes, this technology provides avery compact embodiment and permits the gun to be subjected to a high vibration process without affecting adversely the production of the discharge with this distance between the electrodes.

Other gases than deuterium and other impregnation metals than titanium may, of course, also be employed, if desired, within the scope of the invention.

What is claimed is:

l. A plasma gun comprising a first elongated inner electrode, an elongated insulator member coaxially surrounding said first electrode, and a second electrode enclosing at least a portion of the insulator member and comprising a sintered metal having a quantity of gas adsorbed therein which is releasable to form a plasma, one end of each of said electrodes and said insulator member being arranged in a substantially common plane across which an arc can be established between the electrodes in the plasma.

2. A plasma gun as claimed in claim 1 wherein the sintered electrode further comprises a heating element.

3. A plasma gun as claimed in claim 1 wherein the insulator is bevelled at the one end which lies in said common plane.

4. A plasma gun as claimed in claim 1 wherein said first electrode is rod-shaped and said insulator comprises a ceramic tubular member.

5. A plasma gun as claimed in claim 4 whereina'said second electrode is composed of sintered particles of titanium having dimensions in the range between 40 microns and 100 microns.

6. A plasma gun as claimed in claim 5 wherein the adsorbed gas comprises deuterium.

7. A plasma gun as claimed in claim 4 further comprising a heater element embedded within said sintered electrode for 

1. A plasma gun comprising a first elongated inner electrode, an elongated insulator member coaxially surrounding said first electrode, and a second electrode enclosing at least a portion of the insulator member and comprising a sintered metal having a quantity of gas adsorbed therein which is releasable to form a plasma, one end of each of said electrodes and said insulator member being arranged in a substantially common plane across which an arc can be established between the electrodes in the plasma.
 2. A plasma gun as claimed in claim 1 wherein the sintered electrode further comprises a heating element.
 3. A plasma gun as claimed in claim 1 wherein the insulator is bevelled at the one end which lies in said common plane.
 4. A plasma gun as claimed in claim 1 wherein said first electrode is rod-shaped and said insulator comprises a ceramic tubular member.
 5. A plasma gun as claimed in claim 4 wherein said second electrode is composed of sintered particles of titanium having dimensions in the range between 40 microns and 100 microns.
 6. A plasma gun as claimed in claim 5 wherein the adsorbed gas comprises deuterium.
 7. A plasma gun as claimed in claim 4 further comprising a heater element embedded within said sintered electrode for causing the release of said adsorbed gas and wherein the end of the tubular insulator member lying in said common plane is conically shaped.
 8. A plasma gun as claimed in claim 4 further comprising means for selectively applying a voltage across said electrodes. 